U.S. Pat. No. 3,275,680, Great Britain Pat. No. 1,017,938 and Great Britain Pat. No. 1,117,595 each describe the preparation of benzyl acetate and other benzyl esters wherein an alkyl-substituted phenyl compound such as toluene is reacted in the gaseous phase with an oxygen containing gas, for example, air, acetic acid, and an alkali metal acetate in the presence of a catalyst containing palladium metal supported upon a suitable substrate. The reported quantities of benzyl acetate produced per gram of palladium metal are relatively low. Canadian Pat. No. 820,352 describes a similar process wherein the catalyst contains metallic palladium and gold, and an alkali metal salt such as sodium acetate. Investigation has shown that while this catalyst is much more efficacious than the aforedescribed palladium metal catalysts, there is still considerable room for improvement in process yields.
Great Britain No. 1,328,058 describes a process for preparing benzyl acetate by the reaction of toluene, oxygen and acetic acid in the gaseous phase at an elevated temperature in the presence of a supported catalyst system containing an oxide, hydroxide or carboxylate of palladium and bismuth, or in the case of palladium, the metal itself, and a hydroxide, carbonate or carboxylate of an alkali metal compound. Other metals, including gold and/or copper, or compounds of these metals which do not contain halogen, sulfur or nitrogen, may be added so as to affect the activity and selectivity of the catalyst. Illustrative of a catalyst system of Great Britain Pat. No. 1,328,058 is one containing palladium metal, bismuth acetate and potassium acetate. Use of this catalyst system in the production of benzyl acetate from toluene has provided, at best, only very modest levels of productivity.
It has now been found that toluene and other aryl alkyl compounds can be selectively catalytically oxidized to benzyl acetate and other such esters using a catalytically effective amount of a catalyst comprising palladium, gold, a metal selected from Group VA of the Periodic Table and optionally, one or more promoters. It is indeed surprising that high selectivity can be obtained using the present inventive process since attempted oxidations of toluene to benzyl acetate using known and conventional catalyst systems have provided extremely low conversions to benzyl acetate. The present process, however, provides high selectivity for production of benzyl acetate and other such esters. The yield of these esters realized by the present invention affords a process which is amenable to commercial production of benzyl acetate, a valuable chemical product and intermediate, and such esters in general.